Cu K-edge X-ray absorption study of Fe-doped Bi2Ca1Sr2Cu2Oy superconductors
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XANES
Absorption edge
Lattice constant
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X-ray absorption spectroscopy
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X-ray diffraction patterns and LIII-edge x-ray absorption near edge structure (XANES) spectra of YbInAu2 and LuInAu2 compounds have been measured at high pressure and room temperature using a diamond anvil cell and a synchrotron radiation at SPring-8. YbInAu2 is more compressible at pressures lower than 4GPa than above it; the evaluated bulk modulus by Birch-type equation of state is 54.7GPa which is one-half of that of the LuInAu2 (112.5GPa). The mean valence v¯ of Yb ion in YbInAu2 determined by the XANES measurement is an increasing function of pressure: 2.71(2) at normal pressure and 2.94(2) at 10GPa. The rate of increase in v¯ with pressure is two times larger at pressures below 4GPa than that above 4GPa. However, the v¯ is described by a linear increasing function of the lattice compression: v¯=v¯0+2.9∣ΔV∕V0∣ where v¯0 is 2.71. The extrapolation to the trivalent state gives the critical pressure of 13GPa.
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Absorption edge
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Lattice constant
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X-ray absorption spectroscopy
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ABSTRACT XAS (X-ray absorption spectroscopy) has proven to be a powerful technique in several fields including the biological and environmental sciences. It has enabled scientists to analyze samples that could not be analyzed using classical techniques such as XRD (X-ray diffraction). In addition, it allows for the direct determination of elemental oxidation states, where the use of other methods is time consuming, cumbersome, and can lead to false results. XAS experimentation has allowed the direct determination of the local coordination environments in many different samples. This review article briefly explains some of the concepts related to two of the most important techniques of XAS, which are EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure). An explanation of some of the parameters used to obtain XAS data and data reduction from raw spectroscopic data is discussed. Finally, some applied examples are given that has been obtained though the use of XAS in the biological and the environmental fields.
X-ray absorption spectroscopy
XANES
Absorption edge
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The oxidation state of chromium in glasses melted in an air atmosphere with and without refining agents was investigated by Cr K-edge X-ray Absorption Near-Edge Structure (XANES) and optical absorption spectroscopy. A good agreement in the relative proportion of Cr(III) and Cr(VI) is obtained between both methods. We show that the chemical dependence of the absorption coefficient of Cr(III) is less important in XANES than in optical absorption spectroscopy. The comparison of glasses melted under different conditions provides an indirect assessment of the molar extinction coefficient of Cr(VI) in glasses.
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Molar absorptivity
Oxidation state
Absorption edge
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High‐pressure (0–26.7 GPa) Cu K‐edge X‐ray absorption spectroscopy is used to study possible structural modifications of anti‐perovskite‐type copper nitride (Cu 3 N) crystal lattice. The analysis of X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS), based on theoretical full‐multiple‐scattering and single‐scattering approaches, respectively, suggests that at all pressures the local atomic structure of Cu 3 N remains close to that in cubic phase. Therefore, the transition to metal state above 5 GPa, observed previously using pressure‐dependent electrical resistance and optical absorption measurements, is explained by the band gap collapse due to a decrease of the unit cell volume. We found that the lattice parameter of Cu 3 N is reduced by ≈2% upon increasing pressure up to 26.7 GPa, and the structure is restored upon pressure release.
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X-ray absorption spectroscopy
Lattice constant
Absorption edge
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In this paper, the fixed energy X-ray absorption voltammetry (FEXRAV) is introduced. FEXRAV represents a novel in situ X-ray absorption technique for fast and easy preliminary characterization of electrode materials and consists of recording the absorption coefficient at a fixed energy while varying at will the electrode potential. The energy is chosen close to an X-ray absorption edge, in order to give the maximum contrast between different oxidation states of an element. It follows that any shift from the original oxidation state determines a variation of the absorption coefficient. Although the information given by FEXRAV obviously does not supply the detailed information of X-ray absorption near edge structure (XANES) or extended X-ray absorption fine structure (EXAFS), it allows to quickly map the oxidation states of the element under consideration within the selected potential windows. This leads to the rapid screening of several systems under different experimental conditions (e.g., nature of the electrolyte, potential window) and is preliminary to more deep X-ray absorption spectroscopy (XAS) characterizations, like XANES or EXAFS. In addition, the time-length of the experiment is much shorter than a series of XAS spectra and opens the door to kinetic analysis.
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X-ray absorption spectroscopy
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Absorption edge
Oxidation state
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The codeposition of O2 and Cs on different substrates has been studied by means of near-edge X-ray absorption fine-structure (NEXAFS) experiments. A multiple-scattering analysis shows that the material formed has a tetragonal CsO2 structure with an O-O distance between 1.35 and 1.40 Å. About 19 shells (52 atoms) are necessary to reproduce the oxygen K-edge absorption spectrum of this superoxide, in contrast with recent results by Ruckman et al. (Phys. Rev. Lett., 67 (1991) 2533) which are based on a free-ion calculation.
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Tetragonal crystal system
Absorption edge
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Abstract The method deriving the L self-absorption spectrum from Lα,β emission spectra obtained at different accelerating voltages has been optimized for analyzing the chemical state of Fe in solid materials. Fe Lα,β emission spectra obtained are fitted using Pseudo-Voigt functions and normalized by the integrated intensity of each Fe Ll line, which is not affected by L2,3 absorption edge. The self-absorption spectrum is calculated by dividing the normalized intensity profile collected at low accelerating voltage by that collected at a higher accelerating voltage. The obtained profile is referred to as soft X-ray self-absorption structure (SX-SAS). This method is applied to six Fe-based materials (Fe metal, FeO, Fe3O4, Fe2O3, FeS and FeS2) to observe different chemical states of Fe in those materials. By comparing the self-absorption spectra of iron oxides, one can observe the L3 absorption peak structure shows a shift to the higher energy side as ferric (3+) Fe increases with respect to ferrous (+2) Fe. The intensity profiles of self-absorption spectra of metallic Fe and FeS2 shows shoulder structures between the L3 and L2 absorption peaks, which were not observed in spectra of Fe oxides. These results indicate that the SX-SAS technique is useful to examine X-ray absorption structure as a means to understand the chemical states of transition metal elements.
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Absorption edge
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